Geneva movement for motion-picture projectors



June 1950 M. w. GIESKIENG 2,512,894

GENEVA MOVEMENT FOR MOTION-PICTURE PROJECTORS v 2 Sheets-Sheet 1 Filed Nov. 12, 1946 June 27, 1950 w, G|ESK|ENG 2,512,894

GENEVA MOVEMENT FOR MOTION-PICTURE PROJECTORS Filed Nov. 12, 1946 2 Sheets-Sheet 2 ATTORNEY.

Patented June 27, 1950 UNITED STATES PATENT OFFICE GENEVA MOVEMENT FORMOTION-PIGTURE I PnoJEcTons Marion W. Gieskieng, Denver, Colo. Application November 12, 1946, SerialNo. 709,118 1 Claim. (01. 74- 436) h s inven i n relates to at G neva mov e for motion p cture pro ecto s The thodo Gene a mov ment, as us d in motion pic ure equipment, contains a star wheel and a cam which carries a cam. pin. T e s a eel is pr v d with strai ht, d ametrically extend n cam pinslots. uch Gehevamove n crea a uniform raph. curve in wh ch. h acceleration and decelerati n o the a wheel are ex ly e ual, bo h hei aeomnera velvr p d- T e p d deceleration eft emovem nt o the filmin a ca er o n oie tor as atehoeney o aus t e due o its iner ia tooverride the pr f mins po i ion. To overcome t is t d n y. e cessive frietiohalbrak ne mus be a p ied to th fi m toabrihs it t restlra ly endpr ve ve din The conventiona m i n p c u film feeds throu h the projecto at 9 fee p nu an st r th peak of star whee mov men it 1 v ing at the rate of LBSOfeet per minute. The frictionalhralri re uired tor th sho t dec a p riod of the conventional movement is so excessive ,that it rea ese ea s t ce o the acceleration. o the film to re ul in exce s film wear and dama efh princ pal ob ect of this v t n is to pr vide an improved Geneva movement which will giv amore gradual deceleration to the star wheel the or hodo movement s h e fi m ay be brought to rest with ri inimum of frictional rakin Inth r elieving the brakin friction on the film,thedamae due to rap d acceleration will be eliminated, or at least greatly reduced. No great amountof stress is involved in acceleratin the film from a "stati position a d bringing it to its maximum velocity, for the film itself is very lighteweight andfree-flowing unless braking-tor irictional resistance is applied thereto. Therefore, since this invention reduces the necessity for braking friction by increasing the deceleration period, wear and damage to the film will bereduced to the minimum.

Other objectsand advantages reside in the detail construction of the invention, which is designed for simplicity, economy, and efilciency. These will become more apparent from the following description.

In the following detailed description of the invention-reference is had to the accompanying drawing which forms a part hereof. Like numerals refer to like parts in all views of the drawing and throughout the description.

In the drawings:

Fig. 1 is a fragmentary side elevation of the type of Geneva movement employed in the conventional motion picture projector;

Fig. 2 is a vertical section therethrough, taken on the line 2--2, Fig. 1, in which the various center points are indicated by intersecting location lines;

Figs. 3, 4, and 5 ar position diagrams, indicatii s three given posi ions of th m m nt:

Fig. his a raph chart illu trat ng e eece ere tieh and. d c e ation curve of, the co ve tional Geneva gear in broker-i line, andthe corresponll ins cu ve the mproved Geneva g a in solid lin k his 71s d tail p rspec ive viewii l teti ie'je ir o m w ieh avbe usedwith the impr ved movem and i 8 is a sim lar v e l u a ing a t p to? sta wheel i h istus d with the am o Fi Ih Fi s- 1 and .2, l is of onv. tional fieh a movem nt as. usedin m ti n pieturespror leotor are de ie. ed by .t m.eral as ,iel ows sha l9; seer ll; team plate l2; cam I3; cam pin l4; star wheel shaftlli; star wh el L6- The improved movemen .one ate in the con.- ventienal manner, that is. the camshaft :l u .ro-t tates continuousl and the circumferenceofthfl cam successively centers four arcuated pressions 11 formed in the .SIMI'WIELQBI L6. During 9 :of

each revolution of ithecam shaft .52 the pm i! however, the pinsreceiving slots A8 are curvated ina idiree nr approach .eoncentricit with the circumference of thecam 1 l 3. The. arc. er the .slots 48 changes ,therelative time intervals ofacoeleration and deceleration of-the star wheel. The greateruthe,curvaturauorthe shorter the radius of the arc, the greater will be the acceleration and the more gradual the deceleration.

:Ithas been found experiment that the most satisfactory radius for the arcof the slots 181s twice the radiusRpofthe circle described bythe pin M, as indicated-by the center points A in Fig. 2. The center points A are positioned on center lines which will intersect the axis of the cam shaft t9 and cut the points of entrance andex it of the .pin I4 :from the slots 18 whentha star wheelis at rest, rats/indicated hythe center lines A-.=-b in Fig. 2.

With the center points for the radii of the slots 18 being positioned on the lines A-b, and with radii of twice the diameter of the cycle traveled 3 a total of 45, as shown in Fig. 4, will rotate the star wheel 58, as compared with the 45 of the conventional Geneva movement. Thus the acceleration has been increased.

An additional 22 rotation of the cam, or a total of 6'7 A", as shown in Fig. 5, rotates the star wheel 86, as compared with the 82%; rotation of the conventional, straight-slotted star wheel.

It can be seen from this that a greater period of time is taken for decelerating the speed of the star wheel than is taken for accelerating the speed thereof. This is indicated graphically in the chart of Fig. 6, in which the curve .C indicates the curve of the conventional Geneva movement, and the curve D indicates the curve of the improved Geneva movement.

It will be noted that the star wheel and the film inthe projector will be brought to rest much more gradually than with the conventional movement. At 65 rotation of the cam the improved movement has cut the deceleration curve of the old movement in half. Therefore, only one-half the usual frictional braking is required upon the film to prevent it from overrunning or overshooting its proper framing position, with the resulting jumping of the projected picture.

Since less frictional braking is required on the film, it will have much less resistance to acceleration at the beginning of its movement. The reduction of this resistance greatly reduces the starting strain and resulting wear and tear upon the film.

The relative degrees of movement of the improved Geneva gear and the conventional Geneva gear, as given herein, have been determined from measurements of an actual working model. They have not been determined mathematically. There may be, therefore, a slight variation either way,

' due to errors in measurement and in construction.

The star wheel in the improved movement comes out of the cam at a much slower rate than the conventional Geneva movement, depending upon the radius of the arc of the pin slots. Due to this the trailing extremity of the cam approaches exceedingly close to the forward side of the pin slot in the star wheel. With a radius of 2R and a 90 cam opening there is just suificient clearance for the two parts to pass each other. With a radius of less than 2R, however, the conventional 90 cam opening would not clear the exiting star wheel. The cam opening cannot be increased, as this would tend to inaccuracy in the alignment of the pin slot with the incoming pin.

'- Therefore, for shorter radius slots, means must be provided for preventing interference at this point. This is accomplished by inclining the ends .of the forward sides of the slots I8 at an angle of approximately 45, as indicated at IS in Fig. 8, and by correspondingly inclining the trailing end of the cam l3, as indicated at 20 in Fig. 7. This, ineffect, widens the gap in the cam, for until the two. inclines I9 and 20 align with each other, the star wheel may rotate outwardly. It does not interfere with the accuracy of the cam surface in holding the star wheel through 270 of rotation of the cam, since the length of the long side of the cam surface and the length of the arcuate depressions I! remain the same.

It is desired to call attention to the fact that the pin [4 enters and exits from the slots l8 tangentially, since the circumference of the circle traveled by the pin [4 and the circumference of the arc of the slots I8 coincide at the point of entrance and exit. Therefore, there is no move ment of the star wheel at the instant of entering or leaving the slots.

While'a specific form of the improvement has been described and illustrated herein, it is desired to be understood that the same may be varied, within the scope of the appended claim, without departing from the spirit of the invention.

Having thus described the invention, what is claimed and desired secured by Letters Patent is: A Geneva movement comprising a rotatable cylindrical cam having an end plate and an arcuate circumferentially extending marginal wall having its ends spaced from each other said end plate having an extension projecting from the open side of the marginal wall radially of the end plate and adjacent its outer and carrying a laterally projecting pin parallel to the axis of the end plate, a star wheel rotatable about an axis parallel to the axis of the cam and having its periphery formed with four arcuate recesses having their ends spaced from each other equal distances circumferentially thereoflthe arcuate wall of the cam successively'lying in said recesses and in close fitting face to face engagement with arcuate edges of the recesses, and said star wheel being formed with four longitudinally arcuate slots extending from portions of its periphery between spaced ends of the recesses, outer ends of oppositely disposed ones of said slots having their outer ends disposed in ofiset relation to a diameter of the star wheel and their inner portions crossing the said diameter, and each slot consti= tuting an arc of a circle having a radius twice the radius of the circle followed by said pin during rotation of the cam and movement of the pin into and out of successive slots to impart intermittent rotation to the star wheel.

MARION W. GIESKIEN G.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain Feb. 9,1937. 

